The present invention relates generally to casting processes and, in particular, to a quick-change lock assembly for a casting machine fill tube, where the casting machine preferably utilizes a Vacuum Riserless Casting/Pressure Riserless Casting (VRC/PRC) process.
Casting machines utilizing various processes for producing casts from molds of molten metal such as aluminum to produce articles such as vehicle wheels and the like are well known. In traditional permanent mold processes, metal is melted and poured into a mold having a cavity disposed therein to form the casting. This traditional permanent mold process is disadvantageous because of poor and inconsistent cast quality. More recently, counter gravity casting processes, including low pressure permanent mold casting, have been utilized to improve the quality of the cast product. Counter gravity casting processes typically include a furnace for melting the metal, a mold for forming the cast product, and a riser providing a path for the molten metal to flow from the furnace to the mold. The furnace is typically located below the mold and the molten metal is forced from the furnace into the mold via pressurized gas or an electromagnetic pump.
Casting machines utilizing VRC/PRC processes are a more recent development and are an improvement upon low pressure permanent mold casting processes. As in low pressure permanent mold casting machines, the molten metal is pressurized into the mold but the VRC/PRC process also involves creating a vacuum in the mold cavity before forcing the molten metal into the mold. By creating a vacuum in the mold cavity, the number of risers needed for the casting process and thus the price for the casting machine is reduced. The VRC/PRC process also provides a cleaner and better quality casting than prior art low pressure permanent mold casting machines.
The risers, however, are not completely eliminated and there is a piping connection between the furnace and the mold, known in the art as a fill tube. The fill tubes are typically attached to the bottom surface of the mold with four bolts. Thermal expansions of the bolts are intended to decrease surface pressure between the gasket, the bottom of the mold, and the fill tubes. A typical prior art casting machine utilizing a VRC/PRC process for molten aluminum alloys uses titanium fill tubes. Because titanium fill tubes are very expensive and to reduce contamination of the fill tubes, the interior surface of the fill tube is protected by spraying or by dipping into a coating solution, such as a ceramic insert or the like.
Frequently, a fill tube needs to be replaced because of maintenance, wear, or detected leakage. Replacing the fill tube is an arduous procedure. Because of the heat of the casting process and other concerns, one person is required to hold one guiding device to ensure gasket positioning and align the flanges from below the mold, a second person is required to hold a preheat tube with a graphite gasket and align the flanges from above the mold, and a third person is required to secure the fill tube to the flanges by tightening the mounting bolts. Three workers, therefore, are required for this process. The removal of the fill tubes is very difficult. Often mounting bolts break, slowing the process. The time needed to connect one fill tube in prior art casting machines is approximately six minutes, while disconnecting one fill tube requires four minutes. These two operations combine to make a total of ten minutes of down time to change one fill tube.
It is desirable, therefore, to reduce the amount of time required to connect and disconnect the fill tube for a casting machine utilizing a VRC/PRC process.
The present invention concerns a quick-change lock assembly for releasably attaching a fill tube to a mold in a casting machine. Preferably, the casting machine utilizes a Vacuum Riserless Casting/Pressure Riserless Casting (VRC/PRC) process. The fill tube connects a furnace of the casting machine to the mold. The lock assembly includes an upper ring that is adapted to be attached adjacent an aperture in a surface of the mold of the casting machine. The outer ring has inner and outer concentric surfaces. The lock assembly also includes a lower ring that also has inner and outer concentric surfaces. The inner surface of the lower ring is operable to receive a fill tube. The outer surface of the lower ring is operable to be releasably attached to the inner surface of the upper ring. The lower ring is releasably attached to the upper ring by a ramped portion on the inner surface of the upper ring that engages with a plurality of projection portions extending radially outwardly and axially upwardly from the outer surface of the lower ring. The upper ring is rigidly attached to the surface of the mold with a plurality of fasteners.
In operation, the upper ring is attached to the surface of the mold by a plurality of fasteners and the fill tube is received by the inner surface of the lower ring. The lower ring and the fill tube, when attached, form a tube assembly. The lower ring is then attached to the inner surface of the upper ring, the fill tube extends through the aperture into the mold and the lower ring seals the fill tube to allow molten material to flow from the furnace and though the fill tube into the mold without leaking. The quick-change lock assembly advantageously prevents air from entering mold cavity and prevents molten material from leaking outside the fill tube. Preferably, a gasket is interposed between a sealing surface of the mold and an upper surface of the fill tube. Preferably, another gasket is interposed between an upper portion of the inner surface of the lower ring and another surface of the fill tube. The gaskets are preferably composed of graphite or similar sealing material. Alternatively, the gaskets are a wave spring type gasket.
During operation of the casting machine, the fill tube will need to be changed due to the inevitable development of leaks because of gasket failure and the like. The tube assembly is replaced by first preheating the assembly to a predetermined temperature, preferably 400 degrees Fahrenheit. Prior to connecting this tube assembly the bottom of the mold is preheated to a predetermined temperature, preferably 800 degrees Fahrenheit. The tube assembly is then attached to the lower surface of the mold by turning the assembly in an engaging direction.
The quick-change lock assembly in accordance with the present invention solves several important problems in prior art casting machines utilizing the VRC/PRC process. The assembly provides even gasket compression by utilizing the geometry of the ramped portions. The lock assembly also accepts deviation caused in machining tubes, which are within the tolerance field. Furthermore, the design of the present invention advantageously requires only one person to connect and disconnect the fill tubes. The one person can change a fill tube in a reduced time of approximately four minutes, compared to ten minutes and three workers required in the prior art. In operation, the assembly in accordance with the present invention has reduced the average downtime per day by half, has reduced the average number of tube failures per day by over half and has increased the number of cast products produced per tube by four times.
The quick-change lock assembly of the present invention requires fewer maintenance workers to change a fill tube, reduces down time when an assembly needs to be changed, and provides a measurable cost savings because fewer and quicker changes result in less fill tubes being utilized and more time available to produce the cast product.